The efficient harvesting and delivery of renewable energy supplies are the future of sustainable energy production. Energy storage is critical to enable a stable supply of energy from available energy resources. With the current growth in need of portable consumer electronics, it demands much safer, high-density, light-weight, compact batteries. Although lithium-ion (Li-ion) batteries are widely used in portable electronics, their large scale application is still limited by low energy density, relative high cost of material production, and safety issues. Replacing carbonate based electrolytes by non-volatile and thermally stable solid electrolytes is one of the solutions to solve the crucial problems currently associated with liquid electrolytes. Although solid electrolytes are non-flammable, their low ionic conductivities, relative high activation energy, and interfacial resistance hinder their practical applications.
The ionic conductivity of solid electrolytes usually changes dramatically with temperature because of the relatively high activation energy of solid electrolytes. Stable performance under changing temperature environments in a solid state device is a great challenge. Therefore, low activation energy in a material is crucial to achieve consistent performance of the device in a broad temperature range, especially below room temperature. Similarly, high activation energy in a solid state device could give rise to serious issues in material processing under changing temperature environments. Therefore, low activation energy in a material is necessary to achieve consistent performance of the device in a broad temperature range especially below room temperature.
Interfacial resistance is another important factor that cannot be ignored when it comes to the practical application of solid electrolytes in all-solid-state devices. For example, a fast lithium superionic conductor Li10GeP2S12 has been reported by Kamaya et al., the conductivity of which reached 10−2 S cm−1 at room temperature. Since the lithium ion transference number in this solid electrolyte is unity, the lithium ion conductivity is even higher than carbonate-based liquid electrolytes. However, metallic Li compatibility still remains a challenge to be resolved.